Fluorocarbon and fluorohydrocarbon polymers are known for their properties of chemical and thermal resistance. However, their processing in comparison to non-fluorinated polyalkanes is typically more difficult and complex. For example, polytetrafluoroethylene cannot be processed by standard melt state techniques since at the high temperatures necessary to obtain a reasonable viscosity, it degrades too rapidly. Consequently, it is processed in ways similar to metal processing such as by the sintering of preshaped items formed from powders or of thin layers deposited from water borne dispersions.
Partially fluorinated polymers such as polyvinylidene fluoride are generally processable using melt techniques commonly applicable to thermoplastic hydrocarbon polymers. Higher temperatures and special equipment made of corrosion resistant alloys are required, however. Partially fluorinated rubbers can also be crosslinked by using bifunctional nucleophilic reactants such as telechelic diamines or big-phenols. Formulations are typically complex including several inorganic bases and accelerators. Also careful control of temperature during both crosslinking and post cure phases of the process is required. Other partially fluorinated copolymers with units containing bromo or iodo substitiuents have been developed which can be vulcanized by peroxides in the presence of triallylisocyanurate.
Elastomers prepared by crosslinking fluorohydrocarbon polymers have superior thermomechanical and chemical resistance relative to hydrocarbon rubbers, but are limited by a service temperature of 150.degree. C. under high compression or tensile load due to creep and relaxation phenomena. Thermal oxidative resistance is very good up to 260.degree. C. to 350.degree. C.
While the chemical and physical modification of hydrocarbon polymers has been quite extensively studied, so that many commercial products are available as blends, alloys, grafted copolymers, block copolymers, radiation crosslinked polymers etc., relatively little effort has been devoted to such methods of modifying fluorocarbon and fluorohydrocarbon polymers.
Accordingly, it is an object of this invention to provide a process for modifying fluorohydrocarbon polymers by the introduction of unique substituents alone the polymer chain. It is a further object to provide fluorohydrocarbon polymers having substituents containing reactive groups which will facilitate further controlled reaction and modification of the polymers in processes for blending, alloying, and crosslinking of the polymers.
The crosslinking reaction of vinylidene fluoride (VDF)-hexafluoropropene (HFP) copolymers has been reviewed by Cirillo et al., Biological and Synthetic Polymer Networks, 1988, 255. Specifically, crosslinking is characterized as a sequence of reactions with first a base-induced dehydrofluorination producing polymer chain unsaturation and then network formation by reaction of the unsaturated chains with a bisnucleophile. Cirillo et al. studied the reaction by isolating the unsaturated polymer and reacting it with reagents such as bromine and p-chlorophenate to evaluate the characteristics of the unsaturated sites of the polymer.
A method for grafting organopolysiloxane segments to fluorocarbon polymeric segments is described in U.S. Pat. No. 4,314,043. Generally, both fluorocarbon polymer segments and organopolysiloxane segments are first prepared with reactive sites and then combined under conditions such that the reactive sites co-react to bind the fluorocarbon polymer and organopolysiloxane segments together. However, a graft copolymer was also prepared by refluxing in methylethylketone a vinylidine fluoride-co- hexafluoropropylene polymer with an organopolysiloxane polymer containing ethylene diamine functional substituents.
Brennan et al., Polym. Prepr. (Am. Chem. Soc.) 1988, 29(2), 336, reports surface modification of polyvinylidene fluoride whereby groups such as --OH, --NH.sub.2, --CN, Br, or Cl are attached to the polymer chain at the surface interface. In a related investigation Dias et al., Polym. Prepr. (Am. Chem. Soc.) 1986, 27(2), 44, described additional studies directed to the introduction of functional groups on the surface of polymers such as polyvinylidene fluoride and polytetrafluoroethylene.